"What's this? Kyaaaa!!! Wh-Why did I suddenly turn into a beanpole?!”

Choi Yeong-Jik was a food and nutrition academic nerd. I am a certified fitness enthusiast with a first-grade qualification in lifestyle sports instruction. But then one morning, waking up with all his bountiful muscles gone, he finds himself in the body of Grand Prince Su-Yang, the second child of Se-Jong the Great. Unable to hide his excitement at the thought of seeing the Great King Se-Jong in person and wondering whether it is a dream or reality, Yeong-Jik goes to see his father, the Great King Se-Jong.

"Uh...? Is this the Great King... Se-Jong?"

Before him sits a pot-bellied man who looks like he's having trouble even breathing. What on earth is this?

The Great King Se-Jong is severely obese and diabetic, and all the officials are suffering from chronic illnesses. Having been a fitness trainer for 15 years, the gym rat pride of Choi Yeong-Jik begins to ignite passionately.

“Well, shall we spread the fitness fever in Joseon for once?! "

(Source: KakaoPage, translated)